Integrated circuit technology enables circuit manufacturers to place increasingly large numbers of electrical devices into smaller silicon chips. Similarly, these chips are packaged and mounted on an increasingly higher density circuit board. The larger number of devices within a smaller area of circuit board has led to significant advances in circuit performance. It has also led to significant problems associated with maintaining the circuits in a low enough temperature range to enable the circuits to operate at such high performance. Typically, the circuits and circuit boards are cooled by forced air. However, efficiently removing heat from circuit boards requires a high degree of uniformity across the boards and a high heat removal rate. Forced air systems have difficulty meeting these requirements as the circuit density becomes greater. Specifically, a relatively large space between the boards is required to permit sufficient air flow between the boards. Also, two edges of the boards must be left open (i.e. free of obstructions such as interconnections) to permit the air to pass between the boards and cool the board surfaces. This decreases the interconnectivity between boards because those two sides are not available for electrical connections.
Prior art attempts to cool high density integrated circuitry have primarily focused on two areas. The first area is immersing the integrated circuits into a coolant while the circuits are in operation. The advantage of this method of cooling is that the heat transfer coefficient of the coolant can be several orders of magnitude greater than that of air. The coolant can remove greater amounts of heat and therefore more easily maintain the temperature of the circuits within a suitable range. The problem with this method of cooling is that the coolant itself can affect the electrical performance and reliability of the integrated circuit. Immersion in a coolant requires the circuit connections and the circuits to be resistant to not only the immersion in the coolant but also the corrosive effects of the coolant. Additionally, immersion in a container requires a complete shutdown of the system to service a single board in a multi-board system. This is an expensive and complicated method to cool and service the electrical system.
A second focus area in the prior art involves placing integrated circuits adjacent to heat conducting metal bodies which contain a fluid flow. The fluid flow removes the heat but does not immerse the integrated circuit in the coolant. The advantage of this system is that it avoids the reliability problems of immersing the circuits in the coolant. The problem with this method of cooling is that it is not as efficient in removing heat from the circuits as the immersion technique. The reason for this lack of cooling efficiency is that the metal body does not contact a sufficient area of the integrated circuits to rapidly transfer heat away from the integrated circuit. The lack of cooling surface area results from the complexity of producing a heat sink for an entire circuit board. That is, merely the tops of circuit modules are cooled because it is too difficult to cheaply manufacture fluid channels for the entire topology of the board. Fluid channels are also only typically used on large planar boards in order to minimize the number of fluid channel/board assemblies for packaging a given number of electronic modules. This results in long signal transmission times because signals are transmitted over a long distance on a single board rather than over a shorter distance between different boards. A three dimensional array of interconnected circuit boards shortens signal times when compared to two dimensional planar wiring.